fix(icons): render brand icons under the fa fab double prefix and drop an empty sprite key

FA5's own single-class declarations lose the cascade to the later
.fa,.far,.fas family rule, so zibll-legacy values like "fa fab fa-weixin"
rendered with the Free font and came up blank — visible in the picker's
brand tab (500px…zhihu) and on every brand icon in the SPA and frontend
social links. Re-assert .fa.fab (and .fa.far weight) in the three
stylesheets that load FA5. Also remove the empty aksrt_svgs['qqww']
sprite entry, which surfaced as a blank built-in SVG item.

assets/css/admin-icon-picker.css

@@ -193,3 +193,8 @@
   flex: 1 1 160px;
   min-width: 0;
 }
+
+/* zibll-legacy "fa fab / fa far" double-prefix beats FA5's own single-class
+   declarations in the cascade — re-assert the brand family/regular weight. */
+.fa.fab{font-family:"Font Awesome 5 Brands";font-weight:400}
+.fa.far{font-weight:400}

assets/css/main.css

@@ -14217,3 +14217,9 @@ body.error404 {
 
 
 /*--------------OVER---over---------OVER---over---------OVER---over---------OVER---over-----------*/
+
+/*--------------FA5 family-prefix compatibility---------FA5 family-prefix compatibility-------------*/
+/* zibll-legacy "fa fab / fa far" double-prefix values beat FA5's own single-class
+   declarations in the cascade, blanking brand icons and bolding regular ones. */
+.fa.fab{font-family:"Font Awesome 5 Brands";font-weight:400}
+.fa.far{font-weight:400}